The invention relates to a device for controlling engine torque in response to shifting between gears of a gear speed change transmission driven by an engine.
In a known device of this type (German Patent Specification No. 2,842,389), such switching signals must be used which are timed to occur before the actual shift operation, because a torque reduction even before disengagement of the old gear is aimed for. This necessitates the use of timing elements which can only be matched with difficulty to the shifting operation for controlling both the final control element for the torque reduction and the shift final control elements for shifting.
An object on which the invention is based is to construct a system which facilitates triggering of the engine intervention for torque reduction at the right moment of maximum heat generation in the friction shift final control elements to prevent as great a proportion as possible of the quantities of shifting induced heat which would be otherwise generated with shifting without torque reduction.
This object is achieved according to the invention by providing a control apparatus which automatically generates a switching signal in response to torque reversal at a reaction gear element of the transmission which switching signal is supplied to control the engine torque.
In the apparatus, constructed according to preferred embodiments of the invention, the engine intervention for torque reduction when shifting up is initiated precisely at the start of shifting, that is in the period of greatest heat generation of the shift transmission, whereby a considerable proportion of the quantities of heat which would otherwise be generated are avoided.
In especially preferred embodiments of the invention, a torque reduction before the start of shifting is also deliberately dispensed with when shifting down under load to avoid inevitable timing inaccuracies with regard to controlling the breakaway operation in the shift element to be disengaged. This is so as there is the risk that the torque is decreased even before the actual start of speeding up. This would mean that not only smooth shifting, but also valuable acceleration time would be lost. The gentle downturn in torque at the start of shifting down is achieved simply and reliably in the device according to preferred embodiments of the invention by hydraulic throttling in conjunction with a pressure transducer upon disengagement of the shift element.
The advantages achieved by the devices constructed according to the invention with regard to the reduction in the quantities of shifting or frictional heat are particularly significant in the case of shifting under load.
As the quantities of heat in the friction shift final control elements occurring in the full load range or in the vicinity of the full load range, without torque reduction, constitute a multiple of the quantities of heat generated in the partial load range, in devices according to certain especially preferred embodiments of the invention a blocking of the torque reduction is provided by way of a blocking device operated on by signals which reflect the engine operating load.
In order to be able to use the different signals at a reaction gear element in shifting up to a certain gear on the one hand and shifting up from this gear on the other hand for the control of torque reduction, devices according to certain especially preferred embodiments of the invention include timing elements for controlling the duration of the torque reduction as a function of whether an upshift or a downshift of the transmission is effected.
In order to be able to match the duration of the torque reduction to the different conditions when shifting up on the one hand and when shifting down on the other hand in the device according to especially preferred embodiments of the invention, means are provided for assuring that the time period of torque reduction is shorter for downshifting than for upshifting.
Other advantageous features of the present invention relate to the specific simple electronic circuit components which are used to effect a reliable and economical construction for optimally controlling the engine torque during and shortly after gear shifting operation.
Devices constructed according to specifically preferred embodiments of the invention are simple in construction, and yet precise, because the torque jump at the brake band abutment device of the reaction gear element is used for generating the switching signal.
In devices constructed according to especially preferred embodiments of the invention, it is advantageous that no timing elements are necessary for fixing the start of torque reduction. In this way, the effects of frictional value variations and fluctuating speed-up times of the internal combustion engine, which arise from changes in the engine state, of the oil temperature, of the water temperature, of the air pressure, of the air humidity etc., are completely avoided.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.